This invention relates to a reading, printing and copying device functioning to converting data on an original into electrical signals, reproducing the original from the electrical signals and copying the original, and in which the operational efficiencies of liquid crystal shutters for controlling the copying light beam are improved. Thus, the capacity of the light source, namely, a lamp is reduced.
A patent application entitled "A reading, printing and copying device" filed on the same day as this application, commonly assigned, Ser. No. 548,490 describes a device shown in FIGS. 1(a) and 1(b) herein. As shown in FIG. 1(a) and FIG. 1(b), split electrodes made of a metal film of Cr, Al, Ni or Au are formed on a transparent substrate 1 of glass or the like and are covered by a photo-conductive layer 3 of semiconductor material such as amorphous-Si, Se--As--Te or CdS. A transparent conductive film 4 of ITO or SnO.sub.2 is formed on the photo-conductive layer 3 and is connect to an electrode 5. The split electrodes 2 are connected to transparent conductive films 6 which are made of the same material as the transparent conductive film 4. A liquid crystal 7 surrounded by seal members 8 and sealed by a transparent conductive film 9 is provided on the transparent conductive films 6. Polarizing plates 10 and 11 are provided on the surface of the transparent conductive film 9 and the rear surface of the substrate 1, respectively. The transparent conductive films 6 are connected to electrodes 12 formed on the substrate 1, which are connected to a drive circuit 14 through lead wires 13. In the device thus constructed, portion 20 functions as a film image sensor, portion 21 as a liquid crystal shutter, and portion 22 as a drive unit.
FIG. 2 is a circuit diagram showing the device in FIG. 1(a) and FIG. 1(b). The device comprises: film image sensors 20a, 20b, 20c and 20d each being a parallel circuit of a resistor and a capacitor; liquid crystal shutters 21a, 21b, 21c and 21d having first terminals connected to a bias source 25 (having a bias potential V.sub.B) and second terminals connected to electrodes 36 (corresponding to the split electrodes 2, the transparent conductive films 6, the electrodes 12 and the lead wires 13); a MOS transistor 24 connected through the electrode 5 to the film image sensors 20a, 20b, 20c and 20d, for receiving a signal C (the transistor 24 being rendered conductive when the signal C is "high 1"); MOS transistors 30a, 30b, 30c and 30d whose control terminals are connected to terminals D, F, H and J of a shift register 27, the transistors 30a through 30d applying the bias potential V.sub.A to the electrodes 36 when rendered conductive; and MOS transistors 31a, 31b, 31c and 31d whose control terminals are connected to terminals E, G, I and K of the shift register 27. The transistors 31a through 31d are adapted to control the connection to MOS transistors 29 and 34. The MOS transistor 29 receives a signal B. When the signal B is "1", the MOS transistor 29 is rendered conductive, so that the state of the electrode 36, after being amplified by an amplifier 35, is outputted, as a signal N, from the terminal 37. The MOS transistor 34 receives a signal A. When the signal A is "1", the transistor 34 is rendered conductive, so that a signal L is applied through the terminal 33 to the electrode 36.
The operation of the device organized as illustrated in FIG. 2 will be described.
(1) Operation of converting data on an original into electrical signals (FIG. 3):
Assume first that signals "low 0", "1" and "1" are applied, as the signals A, B and C, to the control terminals 32, 28 and 23 of the MOS transistors 34, 29 and 24, respectively. In this case, the MOS transistor 34 is turned off, and the MOS transistors 29 and 24 are turned on. When, in the case where signals D through K having a period T are applied from the shift register 27 through the terminals D through K to the control terminals of the MOS transistors 30a through 30d and 31a through 31d, the signal D is "1" (as indicated at waveform D pulse i), the MOS transistor 30a is turned on. As a result, the capacitor of the film image sensor 20a is charged to the potential V.sub.A by the bias source 26.
When the signal D is set to "0" (as indicated at ii), the MOS transistor 30a is turned off. When the film image sensor 20a is illuminated upon illumination of the original, the resistance of the photoconductive film 3 is decreased to allow a photocurrent ip (FIG. 2) to flow in the sensor, so that the charge potential V.sub.A is decreased towards a potential V.sub.S. When the signal E is raised to "1" (as indicated at i) next pulse, the MOS transistor 31a is turned on. As a result, the potential of the electrode 36 which has been decreased to V.sub.S is provided, as the signal N, at the terminal 37 through the MOS transistor 29 which is conductive and the amplifier 35. When the signal F is raised to "1", the film image sensor 20b is similarly charged to V.sub.A. If it is not illuminated according to the state of the original, the potential V.sub.A is maintained unchanged. Therefore, when the signal G is raised to " 1" (as indicated at i), the potential V.sub.A is outputted, as the signal N, from the terminal 37. As the above-described operation is repeatedly carried out, the signals N are outputted from the terminal 37 in response to the illumination of the film image sensors 21a through 21d.
(2) Operation of reproducing an original from electrical signals (FIG. 4):
When signals "1", "0" and "0" are applied, as the signals A, B and C, to the control terminals 32, 28 and 23 of the MOS transistors 34, 29 and 24, respectively, the MOS transistor 34 is turned on and the MOS transistors 29 and 24 are turned off. Signals "0" are applied, as the signals D, F, H and J, to the control terminals of the MOS transistors 30a through 30d through the terminals D, F, H and J by the shift register 27, so that transistors 30a through 30d are rendered non-conductive. When, under this condition, a picture signal L (in which V.sub.C is the high level and 0 is the low level) is applied through the terminal 33 of the MOS transistor 34 and the signals E, G, I and K timed as shown in FIG. 4 are applied to the control terminals of the MOS transistors 31a through 31d through the terminals E, G, I and K from the shift register 27, the liquid crystal shutter 21a becomes transparent (indicated at i) receiving the potential V.sub.B of the bias source 25. This occurs because, when signal E is raised to "1", the MOS transistor 31a is rendered conductive (as indicated at i) so that a signal "0" is applied, as the picture signal L, to the electrode 36. When the signal E is set to "0" (as indicated at ii), the MOS transistor 31a is rendered non-conductive, so that the above-described state is maintained unchanged. When a signal "1" is applied, as the signal G, to the control terminal of the MOS transistor 31b, it is rendered conductive. Therefore, the liquid crystal shutter 21b receives the high level V.sub.C as the picture signal L through the electrode 36, and accordingly the potential difference across the shutter 21b becomes V.sub.B -V.sub.C .apprxeq.0. As a result, the liquid crystal shutter 21b becomes opaque (as indicated at i). When the signal E is raised to "1" again (as indicated at iii), the picture signal L is at the high level V.sub.C, and V.sub.B -V.sub.C is applied to the liquid crystal shutter 21 a. As a result, the liquid crystal shutter 21a becomes opaque. The liquid crystal shutters 21c and 21d can be made transparent and opaque according to the picture signal L when they are controlled by the signals I and K, respectively.
(3) Operation of copying an original (FIG. 5):
A signal 0 is applied, as the signal A, to the control terminal 32 of the MOS transistor 34, a signal "0" is applied, as the signal B, to the control terminal 28 of the MOS transistor 29 and a signal "1" is applied, as the signal C, to the control terminal 23 of the MOS transistor 24, so that the MOS transistors 29 and 34 are turned off while the MOS transistor 24 is turned on. The shift register 27 outputs the signals D, F, H and J. When the signal D is raised to "1" (as indicated at i), the MOS transistor 30a is rendered conductive, so that the capacitor of the film image sensor 20a is charged to the potential V.sub.A by the bias source 26. If the image sensor 20a is illuminated when the MOS transistor 30a is turned off with the signal D set to 0 (as indicated at ii), it is discharged through the MOS transistor 24, and therefore its potential is decreased from the charge potential V.sub.A to the discharge potential V.sub.S.
In response the voltage applied to the liquid crystal shutter 21a is increased from V.sub.B -V.sub.A (i.e., the difference between the potential V.sub.B of the bias source 25 and the charge potential) to V.sub.B -V.sub.S .apprxeq.V.sub.B. When the voltage reaches the threshold value V.sub.T during this increase, the liquid crystal shutter 21a becomes transparent. The state of the liquid crystal shutter 21a is shown in a state diagram T.sub.O in FIG. 5. The liquid crystal shutter 21a is transparent for a period of time T.sub.2 which is shown shaded.
The above description is applicable to the remaining liquid crystal shutters 21b, 21c and 21d. The signals E, G, I and K are maintained at 0 as illustrated in FIG. 5.
In the reading, printing and copying device described above, as is apparent from the transparent state diagram T.sub.O of the liquid crystal shutter 21a, the operation of the liquid crystal shutter becomes effective only for the period of time T.sub.2 which is a portion of the period of time T of one cycle (because of the presence of the pause period of time T.sub.1). Accordingly, it is essential that the capacity of the copying light source such as a lamp is very large.